Described below is a method for transmitting user data between a first communication device, which uses encryption, and a second communication device.
In modern communication systems, realtime voice or video communication frequently takes place over one or more packet-switched, particularly internet protocol based networks. Such a type of voice or video communication is frequently also referred to as VoIP (VoIP: Voice/Video over Internet Protocol).
Since many packet-switched networks, such as the Internet for example, do not on their own initiative offer any reliable protection against listening in by unauthorized persons, provision is frequently made in the case of VoIP communication to encrypt on the user side the voice or video data to be transmitted. In many, particularly heterogeneous, communication systems the particular encryption requirements can however vary from user to user. Thus in a communication system there frequently exist both users who can communicate only in unencrypted fashion, and also users who can communicate in encrypted or unencrypted fashion, and also users who can communicate only in encrypted fashion.
A VoIP communication is frequently routed by way of a plurality of different communication networks. The different communication networks are as a rule coupled to one another by so-called gateway facilities which in the context of the VoIP communication carry out a conversion of the user data to be transmitted with regard to the transfer between the communication networks. Such conversions do however as a rule have a disadvantageous effect on the transmitted voice or video quality.
In order to avoid such a degradation of the voice or video quality, provision can be made to set up a user data direct connection between the communicating users, by which the gateway facilities can at least be logically bypassed. Such a setup of a direct connection is also known as a “Direct Media Connection”.
A direct connection between users having incompatible encryption requirements and capabilities is however not easily possible.